# Online Electronics and Communication Engineering Test - Previous Exam Papers Test 1

Instruction:

• This is a FREE online test. DO NOT pay money to anyone to attend this test.
• Total number of questions : 20.
• Time alloted : 30 minutes.
• Each question carry 1 mark, no negative marks.
• DO NOT refresh the page.
• All the best :-).

1.

As the temperature increases the mobility of electrons __________ .

A.
 decreases because the number of carries increases with increased collisions
B.
 increases because the number of carries decreases with decreased collisions
C.
 remains same
D.
 none of the above

Explanation:

Mobility of electrons

m = 2.5 for electrons and 2.7 for holes in Si.

2.

For the power amplifier circuit shown below, the maximum power dissipated by both output transistor is

A.
 9.66 W
B.
 30.11 W
C.
 31.66 W
D.
 33.66 W

Explanation:

The maximum power dissipated by both output transistor is maximum

3.

A periodic rectangular signal, x(t) has the waveform shown in the given figure. Frequency of the fifth harmonic of its spectrum is __________

A.
 200 Hz
B.
 250 Hz
C.
 400 Hz
D.
 1250 Hz

Explanation:

The periodic time = 4 ms = 4 x 10-3 s

The fundamental frequency

Frequency of the 5th harmonic

= 250 x 5 = 1250 Hz.

4.

In the following limiter circuit, an input voltage V1 = 10 sin 100pt applied. Assume that the diode drop is 0.7 V when it is forward biased. The zener breakdown voltage is 6.8 V

The maximum and minimum values of the output voltage respectively are

A.
 6.1 V, -0.7 V
B.
 0.7 V, -7.5 V
C.
 7.5 V, -0.7 V
D.
 7.5 V, -7.5 V

Explanation:

During +ve part of Vi

D1 will be forward biased

Zener diode is reverse biased

Thus net voltage = 6.8 + 0.7 = 4.5 V

During -ve part of Vi

D2 will be forward biased

D1 will be reversed biased

Thus net voltage = -0.7 V .

5.

Find the value of ix if each resistance is of 3 Ω and each battery is of 6 V.

A.
 1.1428 V
B.
 1.432 A
C.
 0.2892 A
D.
 O A

Explanation:

Using Mesh analysis

Loop 1 : 6 = 9i1 - 3i4 ...(i)

Loop 2: 6 + 6 = - 6i2

i2 = - 2A ...(ii)

Loop 3: 6 = 9i3 - 3i4 ...(iii)

Loop 4: 6 = 9i4 - 3i3 - 3i1 ...(iv)

Solving the above equations simultaneously

i1 = i3 = 1.1428 A

i4 = 1.432 A

ix = i4 - i3 = 0.2892 A.

6.

A 300 MHz plane EM wave is propagating in free space. The wave is incident normally on an infinite copper slap. The antenuation constant for the wave is (σcopper = 5.8 x 107 mho/ m). The skin depth is

A.
 0.005 x 10-3 m
B.
 0.0038 x 10-3m
C.
 0.0028 x 10-3 m
D.
 0.0024 x 10-3 m

Explanation:

.

7.

The Z inverse of the given Z transform is :

A.
 unit step
B.
 unit impulse
C.
 unit ramp
D.
 unit parabola

Explanation:

8.

The probability density function (PDF) of a random variable X is as shown below

The corresponding cumulative distribution function (CDF) has the form

A.
B.
C.
D.

Explanation:

Cumulative distribution function (Pdf) dx

Then when we integrate the line from (-1, 0) to (0, 1) we get a parabolic curve.

The maximum value of Pdf can be 1.

9.

Consider the program segment written for 8085 based system:
LXI S, FFFFH
MVI A, 00H
MVI B, 0FH
SUB B
CNC GOLOC
MVI A, FFH
where in the program subroutine labelled ''GOLOC'' introduces delay of 28 T-states only. How many T-states are required to execute above program statement?

A.
 41
B.
 69
C.
 44
D.
 Indeterminate

Explanation:

Since carry (CY) flag will not be set at the execution of "SUB B" instruction;

check for CY flag fails but this requires 9(= 6 OP - CODE FETCH + 3T - states) T-states

Total T-states = 10 + 7 + 7 + 4 + 9 + 7 = 44.

10.

The magnitude plot of a composite signal x(t) = e3jt + e4jt is __________ .

A.
 Half wave rectified sinusoid
B.
 Full wave rectified sinusoid
C.
 Exponentially increasing sinusoid
D.
 Exponentially decreasing sinusoid

Explanation:

x(t) = ej3.5t(e-j05t + ej0.5t)

x(t) = 2ej3.5t cos(0.5)t

The magnitude of x(t) is |x(t)| = 2|cos(0.5)t|.

11.

In the given figure
.
The damped frequency is __________ .

A.
B.
C.
D.
 None of these

Explanation:

Damped frequency

ωd = 3/2.

12.

The driving point impedance of the following network is given by . The component values are

A.
 L = 5H, R = 0.5Ω, C = 0.1F
B.
 L = 0.1H, R = 0.5Ω, C = 5F
C.
 L = 5H, R = 2Ω, C = 0.1F
D.
 L = 0.1H, R = 2Ω, C = 5F

Explanation:

Comparing it with given equation

C = 0.1

RC = 0.05

R = 0.54

.

13.

The Table given below is the mark obtained by 2 students in 8 different subjects.

The regression line of y on x is:

A.
 y + 0.57x = 9.7558
B.
 y - 0.57x = 9.758
C.
 033y + x = 6.335
D.
 0.33y - x = 6.335

14.

A matched filter has a frequency response given:

The impulse response h(t) of the filter is :

A.
 [δ(t) - δ(t - T]
B.
 [u(t) - u(t - T)]
C.
 [S gn(t) - Sgn(t - t)]
D.
 [S gn(t) + Sgn(t - T)]

15.

Value of 'K' for the system for which the system is stable:

A.
 K < 1
B.
 K > 1
C.
 K < 2
D.
 K > 2

16.

A 3 x 8 decoder with two enable inputs is to be used to address 8 blocks of memory. What will be the size of each memory block when addressed from a sixteen bit bus with two MSBs used to enable the decoder?

A.
 2 K
B.
 4 K
C.
 16 K
D.
 64 K

17.

The following properties are associated with ferroelectric materials:

1. Its susceptibility is negative.
2. The susceptibility is expressed as
where c is the Curie constant and Tc is the Curie temperature.
3. It has permanent dipoles oriented randomly.
Which of the above statements is/are correct?

A.
 1 only
B.
 1 and 3
C.
 2 only
D.
 1, 2 and 3

18.

The circuit shown in the figure is used to charge the capacitor C alternately from two current sources as indicated. The switches S1 and S2 are mechanically coupled and connected as follow
For 2nT ≤ t < (2n + 1)T, (n = 0, 1, 2, ...) S1 to P1 and S2 to P2
For (2n + 1) T ≤ t < (2n + 2)T, (n = 0, 1, 2, ...) S1 to Q1 and S2 to Q2
Assume that the capacitor has zero initial charge. Given that u(t) is a unit step function, the voltage Vc(t) across the capacitor is given be

A.
 (- 1)n tu(t - nT)
B.
 u(t) + 2 (-1)n u(t - nT)
C.
 tu(t) + 2 (-1)n (t - nT) u(t - nT)
D.
 [0.5 - e-(t - 2nT) + 0.5e-(t - 2nT - T) ]

19.

Consider the network: Impedance of this network as a function of the complex frequency is consists of a certain number of zeros and poles. What is the location of poles?

A.
 -2
B.
 -2, ∞
C.
 2
D.
 2, ∞

20.

Assertion (A): The line integral of B about a closed contour, in a region containing steady current, is μ0 times the total net current, following through the contour of integration.

Reason (R): The curl of B is equal to μ0 times the current density vector J

A.
 Both (A) and (R) are true and (R) is the correct explanation of (A)
B.
 Both (A) and (R) are true but (R) is not the correct explanation of (A)
C.
 (A) is true but (R) is false
D.
 (A) is false but (R) is true